Force calling PostDisplayConfigurationChange() even if earyling out in UpdateDisplays

ash/display/display_manager.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ash/display/display_manager.h"
 
 #include <algorithm>
 #include <cmath>
 #include <set>
 #include <string>
@@ skipping 871 matching lines @@
   }
 
   scoped_ptr<NonDesktopDisplayUpdater> non_desktop_display_updater(
       new NonDesktopDisplayUpdater(this, delegate_));
 
   // Do not update |displays_| if there's nothing to be updated. Without this,
   // it will not update the display layout, which causes the bug
   // http://crbug.com/155948.
   if (display_changes.empty() && added_display_indices.empty() &&
       removed_displays.empty()) {
+    // When changing from software mirroring mode to sinlge display mode, it
+    // is possible there is no need to update |displays_| and we early out
+    // here. But we still want to run the PostDisplayConfigurationChange()
+    // cause there are some clients need to act on this, e.g.
+    // TouchTransformerController needs to adjust the TouchTransformer when
+    // switching from dual displays to single display.
+    if (delegate_)

[Yufeng Shen (Slow to review), 2014/09/11 16:24:02]

hmmm, DisplayControllerTest catches this that we must pair
PreDisplayConfigurationChange with PostDisplayConfigurationChange.

Should we also call PreDisplayConfigurationChange() here  ? or should we change
the test ?

[oshima, 2014/09/11 17:19:08]

Yes, it has to be paired. You can move the PreDisplay.. below

[Yufeng Shen (Slow to review), 2014/09/11 18:25:49]

Done.

+      delegate_->PostDisplayConfigurationChange();
     return;
   }
   // Clear focus if the display has been removed, but don't clear focus if
   // the destkop has been moved from one display to another
   // (mirror -> docked, docked -> single internal).
   bool clear_focus =
       !removed_displays.empty() &&
       !(removed_displays.size() == 1 && added_display_indices.size() == 1);
   if (delegate_)
     delegate_->PreDisplayConfigurationChange(clear_focus);
@@ skipping 357 matching lines @@
       new_secondary_origin.Offset(-secondary_bounds.width(), offset);
       break;
   }
   gfx::Insets insets = secondary_display->GetWorkAreaInsets();
   secondary_display->set_bounds(
       gfx::Rect(new_secondary_origin, secondary_bounds.size()));
   secondary_display->UpdateWorkAreaFromInsets(insets);
 }
 
 }  // namespace ash